Variable-delivery hydraulic pump



April 9, 1968 LEDUC ET AL 3,376,822 7 VARIABLE-DELIVERY HYDRAULIC PUMP Filed Jan. 4, 1967 2 Sheets-Sheet 2 A in United States Patent Office France Filed Jan. 4, 1967, Ser. No. 607,188 Claims priority, applizgtion France, Jan. 6, 1966,

3 Claims. (Cl. 103-38) ABSTRACT OF THE DISCLOSURE Multi-piston hydraulic pump comprising a plurality of parallel pistons which are given a reciprocating move ment of variable amplitude by means of a swash plate pivotally mounted on its support wherein the improvement comprises: a first piston bearing on the rear face of the swash plate and sliding in a cylinder bored in the body of said support; a second piston bearing on the front face of said swash plate and sliding in a cylinder bored in the pump body and communicating with a source of pressure; an axial bore extending through both of the pistons and said piston communication one with the other through a orifice drilled through the swash plate.

It is known to vary the angle of the swash plate of a multi-piston hydraulic pump in order to vary the travel of the said pistons and therefore the delivery of the pump.

Hitherto known devices are complicated so that pumps of this type are generally of a very high prime cost and they are not adequately reliable in operation.

The present invention concerns a pump of this type which is simple and reliable in operation.

The hydraulic pump according to the present invention is a multi-piston swash plate pump wherein the rotation of the said swash plate causes a reciprocating movement of the pistons and wherein the said swash plate is mounted in oscillatory fashion on its support, comprising: a first piston whose head bears on the rear face of the swash plate and which slides in a cylinder formed in the body of the said support of the swash plate coaxially with the driving shaft of the latter; a second piston whose head bears against the front face of the swash plate and which slides in a cylinder formed in the pump body coaxially with the driving shaft of the swash plate, the said cylinder communicating with a source of liquid under pressure, the two pistons being both traversed by an axial bore and communicating with one another through an aperture formed through the swash plate, so that the liquid arriving under pressure in the cylinder of the second piston passes successively through the second piston, the swash plate and the first piston to act on the rear face of the latter in order to vary the inclination of the swash plate.

The present invention also comprises all or part of the following features taken separately or in combination:

(a) The head of the first piston bears on the rear face of the swash plate by means of a stud whose internal diameter is substantially smaller than the diameter of the piston.

(b) The head of the second piston bears on the front face of the swash plate by means of a stud whose internal diameter is slightly less than the diameter of the said piston.

(c) The first piston is of a diameter considerably greater than that of the second piston.

(d) The admission of the liquid under pressure into the cylinder of the second piston can be caused by a 3,376,822 Patented Apr. 9, 1 968 regulating valve controlling the variations of the pump delivery.

By way of example and in order to facilitate the understanding of the invention, in the accompanying drawings:

FIGURE 1 shows a first example of embodiment of the pump according to the present invention.

FIGURE 2 shows a second example of embodiment of a pump according to the invention.

Referring now to FIGURE 1, it will be seen that the multi-piston pump comprises a pump body in two parts 1 and 2. The pistons 3 slide in cylinders 4 constituted by bores formed in the part 2 of the pump casing, and are counter-held by springs 5. A shaft 7 fast with a member 8 serving as a support for a swash plate 9 is journalled in the other part 1 of the pump body, by means of rolling con-tact bearings 6.

The pistons 3 bear in known manner on the front face 9a of the swash plate by means of mobile studs 15.

The swash plate 9 is mounted in oscillatory manner on its support 8 by means of a shaft contained in a plane perpendicular to the axis XX of the shaft 7.

Within the support 8 there is formed a cylinder 11 in which slides a piston 12 through which a bore 13 extends from one side to the other.

The axis of the cylinder 11 and the axis of the bore 13 coincide substantially with the axis XX.

The head 16 of the piston 12 is spherically rounded and bears against the rear face 9b of the swash plate by means of a mobile stud 17. The head 16 of the piston rests on the stud 17 by means of a sphere-conical annular seat whose mean diameter d is substantially smaller than the diameter D of the piston 12. A spring 14 of weak calibration holds the piston 12 hearing against the stud 17 A second piston 22 slides in a bore 21 formed in the part 2 of the pump body, the axis of the bore 21 coincid ing substantially with the axis XX. An axial bore 23 extends right through the piston 22.

The spherically rounded head of the piston 22 bears on the front face 9a of the swash plate by way of a mobile stud 18 on which it rests by means of a spherical or conical annular seat whose mean diameter d is slightly less than the diameter D of the piston 22.

An aperture 19 extends right through the swash plate 9, being arranged in such a manner that its front end debouches within the mobile stud 18 and its rear end within the mobile stud 17.

The bore 21 communicates by way of an orifice 20 with a pressure source not shown here.

The pump thus described operates as follows: when the swash plate is in the position illustrated in FIGURE 2 the liquid, coming from the reservoir, arrives by way of the orifice 24 and then, passing by way of the halfmoon 25 formed on the face 9a of the swash plate 9, enters the pistons 3 and is delivered through the nonreturn valves 26 and the outlet ducts 27.

When pressure liquid arrives from any regulating device, not shown since it does not form part of the invention, by way of the orifice 20, this liquid under pressure passes through the bore 23, the aperture 19, the bore 13 and acts on the rear face of the piston D.

The liquid also acts on the piston 22 but with a very slight force, and this pressure serves only to apply the piston 22 against its stud 18 with sufficient force to ensure sealing-tightness.

Under the influence of the pressure acting on its rear face the piston 12 is displaced towards the right, causing the swash plate 9 to swing about the shaft 10, which has the result of reducing the inclination of the said swash plate 9 and therefore the travel of the pistons 3 and consequently the delivery of the pump.

In proportion as the piston 12 is displaced towards the right, the inclination of the swash plate is diminished until it becomes nil, the delivery of the pump being reduced until it becomes nil.

Thus the delivery of the pump decreases constantly until it becomes nil and it cannot increase again when the swash plate 9 is inclined in the opposite sense because owing to the arrangement of the half-moon 25 on the face 9a of the said swash plate, the admission of the liquid into the pistons 3 would not take place.

FIGURE 1 shows a form of embodiment according to which the delivery of the pump diminishes when the pressure arriving at the orifice 20 increases.

It may be found necessary for the response law to be arranged conversely, the delivery of the pump increasing when the control signal pressure increases. FIGURE 2 represents such a pump.

The pump shown in FIGURE 2 is substantially similar to that shown in FIGURE 1 except for the difference that the inclination of the swash plate is in the inverse ense.

Consequently, in proportion as the pressure arriving through the orifice 20 increases, the inclination of the swash plate and the delivery of the pump increase.

We claim:

1. Multi-piston hydraulic pump comprising a plurality of parallel pistons which are given a reciprocating movement of variable amplitude by means of a swash plate mounted in oscillatory fashion on its support, characterised in that it comprises a first piston whose head bears by means of a mobile stud 0n the rear face of the swash plate and slides in a cylinder formed in the body of the support of the swash plate, substantially coaxially with the driving shaft of the latter; a second piston whose head bears by means of a mobile stud on the front face of the swash plate and which slides in a cylinder formed in the pump body substantially coaxially with the driving shaft of the swash plate, the said last-named cylinder communicating with a source of liquid under pressure; an axial bore extending through both of the pistons and the said pistons communicating with one another through an orifice formed through the swash plate, in such a manner that the liquid arriving under pressure in the cylinder of the second piston passes successively through this second piston, the swash plate and the first piston to act on the rear face of the latter in order to vary the inclination of the swash plate.

2. Multi-piston hydraulic pump according to claim 1, characterised in that the first piston is of a diameter which is considerably greater than that of the second piston.

3. Multi-piston hydraulic pump according to claim 1, characterised in that the liquid under pressure causing modifications of the swash plate angle come from a regulating device which is outside the pump.

References Cited UNITED STATES PATENTS 2,324,524 7/1943 Mercier 103-173 2,611,318 9/1952 Wahlmark 103-l73 2,709,449 5/1955 Garr 103-173 FOREIGN PATENTS 800,403 8/1958 Great Britain.

LAURENCE V. EFNER, Primary Examiner. 

